Odd case failure...at least to me...

[hangunnr]

Got the chance to get out and burn some powder today. Shot several hundred rounds through my DPMS LR308. All was fine till this one was fired. Got peppered with hot gas and shrapnel (no damage to me). The follower in the mag was blown down and lodged sideways in the mag body and the floorplate was set askew. I've run close to 1000 rounds of this load through this gun. The brass was/is twice fired '07 Lake City. I bought this brass new and have only used it in this gun.

I've never seen a case failure like this before. My only guess is that the gun was slightly out of battery but still close enough to fire. Anyone have any insight they'd share as to what happened?

hangunnr

 

[Mc85]

Re: Odd case failure...at least to me...

I had a case failure like that once out of my L1A1. In my case though it just ended up being poorly made early run wolf .308 ammo. After the second case split open I decided the heck with this and packed them up and sent them back to wolf for a no questions refund. I guess in your case it could be just a bad case,or maybe like u said the bolt wasn't fully forward when it went off.

 

[sinister]

Re: Odd case failure...at least to me...

Whoa! Cool.

Looks like your extractor is doing its job. You may be getting a shit-ton (non doctrinal military term) of gas pressure pushing back your carrier group while the case is still obturated against the chamber walls. Most cases won't fail in the groove but rather higher up, where the walls begin at the case head.

Your primer looks OK (no flattening and no raised rim around the firing pin indent).

My guess it's a brass alloy failure.

What's your powder and charge weight? Are you using a Tubb Carrier Weight? That may help delay extraction just a few milliseconds.

 

[BOLTRIPPER]

Re: Odd case failure...at least to me...

I am in the process of reading Hatchers notebook.....


this very thing is addressed and has been seen before.

what happened is the brass is way too SOFT.....at least in the rear of the case about the rim.....

ammo that exibits this manufacturing defect will destroy guns....and could quite possibly injure the shooter.....always wear glasses

 

[JRose]

Re: Odd case failure...at least to me...

Can the DPMS even fire out of battery? I'd say just a bum case.

 

[Greg Langelius *]

Re: Odd case failure...at least to me...

First time I've ever seen one like that; I'm thinking either an early extraction, but more likely, a case quality control failure.

 

[Rhys]

Re: Odd case failure...at least to me...

It's a flaw in the case itself. Early opening will not cause a failure at that point. It is never supported at that point to begin with. My bet would be on a void that was in the case head finaly let go.

 

[Grump]

Re: Odd case failure...at least to me...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rhys</div><div class="ubbcode-body">It's a flaw in the case itself. Early opening will not cause a failure at that point. It is never supported at that point to begin with. My bet would be on a void that was in the case head finaly let go. </div></div>
There's your answer. A latent defect in the metal let go after two firing cycles (you bought it 1x fired, your reload was firing #2, from your description as twice-fired).

Sectioning the piece and looking at it under magnification might reveal whether it was an inclusion/void inside the metal, or a "dent" in the web area which left that part of the extractor groove thinner than spec. I'm not sure, but I believe that localized ammonia embrittlement would show more of a fracture pattern.